From f703385d07e312fd9362087b55d1cf319b6d7df1 Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Sun, 22 Mar 2020 10:57:38 -0600
Subject: [PATCH] fix slaving to JACK transport (again!)

---
 libs/ardour/session_process.cc          | 38 ++++++++++++++-----------
 libs/ardour/transport_master_manager.cc |  9 ++++++
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/libs/ardour/session_process.cc b/libs/ardour/session_process.cc
index b6d7e79bf8..13f2a428ad 100644
--- a/libs/ardour/session_process.cc
+++ b/libs/ardour/session_process.cc
@@ -1109,33 +1109,37 @@ Session::plan_master_strategy_engine (pframes_t nframes, double master_speed, sa
 	sampleoffset_t delta = _transport_sample - master_transport_sample;
 	const bool interesting_transport_state_change_underway = (locate_pending() || declick_in_progress());
 
+	DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK Transport: delta = %1 transport change underway %2 master speed %3\n", delta, interesting_transport_state_change_underway, master_speed));
+
 	if (master_speed == 0) {
 
 		DEBUG_TRACE (DEBUG::Slave, "JACK transport: not moving\n");
 
-		if (!actively_recording()) {
+		const samplecnt_t wlp = worst_latency_preroll_buffer_size_ceil ();
 
-			const samplecnt_t wlp = worst_latency_preroll_buffer_size_ceil ();
+		if (delta != wlp) {
 
-			if (delta != wlp) {
+			DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK transport: need to locate to reduce delta %1 vs %2\n", delta, wlp));
 
-				DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK transport: need to locate to reduce delta %1 vs %2\n", delta, wlp));
+			/* if we're not aligned with the current JACK * time, then jump to it */
 
-				/* if we're not aligned with the current JACK * time, then jump to it */
+			if (!interesting_transport_state_change_underway) {
 
-				if (!interesting_transport_state_change_underway && !tmm.current()->starting()) {
+				const samplepos_t locate_target = master_transport_sample + wlp;
+				DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK transport: jump to master position %1 by locating to %2\n", master_transport_sample, locate_target));
+				/* for JACK transport always stop after the locate (2nd argument == false) */
 
-					const samplepos_t locate_target = master_transport_sample + wlp;
-					DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK transport: jump to master position %1 by locating to %2\n", master_transport_sample, locate_target));
-					/* for JACK transport always stop after the locate (2nd argument == false) */
+				transport_master_strategy.action = TransportMasterLocate;
+				transport_master_strategy.target = locate_target;
+				transport_master_strategy.roll_disposition = MustStop;
 
-					transport_master_strategy.action = TransportMasterLocate;
-					transport_master_strategy.target = master_transport_sample;
-					transport_master_strategy.roll_disposition = MustStop;
+				return 1.0;
 
-				} else {
-					DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK Transport: locate already in process, sts = %1\n", master_transport_sample));
-				}
+			} else {
+				DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK Transport: locate already in process, master @ %1, locating %2 declick %3\n",
+				                                           master_transport_sample, locate_pending(), declick_in_progress()));
+				transport_master_strategy.action = TransportMasterRelax;
+				return 1.0;
 			}
 		}
 
@@ -1143,7 +1147,7 @@ Session::plan_master_strategy_engine (pframes_t nframes, double master_speed, sa
 
 		DEBUG_TRACE (DEBUG::Slave, string_compose ("JACK transport: MOVING at %1\n", master_speed));
 
-		if (_transport_speed) {
+		if (_transport_fsm->rolling()) {
 			/* master is rolling, and we're rolling ... with JACK we should always be perfectly in sync, so ... WTF? */
 			if (delta) {
 				if (remaining_latency_preroll() && worst_latency_preroll()) {
@@ -1152,7 +1156,7 @@ Session::plan_master_strategy_engine (pframes_t nframes, double master_speed, sa
 					transport_master_strategy.action = TransportMasterRelax;
 					return 1.0;
 				} else {
-					cerr << "\n\n\n IMPOSSIBLE! OUT OF SYNC WITH JACK TRANSPORT (rlp = " << remaining_latency_preroll() << " wlp " << worst_latency_preroll() << ")\n\n\n";
+					cerr << "\n\n\n IMPOSSIBLE! OUT OF SYNC (delta = " << delta << ") WITH JACK TRANSPORT (rlp = " << remaining_latency_preroll() << " wlp " << worst_latency_preroll() << ")\n\n\n";
 				}
 			}
 		}
diff --git a/libs/ardour/transport_master_manager.cc b/libs/ardour/transport_master_manager.cc
index 3b3923dc0e..f3083f7af6 100644
--- a/libs/ardour/transport_master_manager.cc
+++ b/libs/ardour/transport_master_manager.cc
@@ -441,6 +441,15 @@ TransportMasterManager::set_current_locked (boost::shared_ptr<TransportMaster> c
 
 	unblock_disk_output ();
 
+	if (c && c->type() == Engine) {
+
+		/* We cannot sync with an already moving JACK transport mechanism, so
+		 * stop it before we start.
+		 */
+
+		AudioEngine::instance()->transport_stop ();
+	}
+
 	DEBUG_TRACE (DEBUG::Slave, string_compose ("current transport master set to %1\n", (c ? c->name() : string ("none"))));
 
 	return 0;